Commutator brush and connection



Oct. 13, 1964 R. M. JOP 3,153,164

COMMUTATOR BRUSH AND CONNECTION Filed May 15, 1961 2 Sheets-Sheet 1 FIG.4

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COMMUTATOR BRUSH AND CONNECTION Filed May 15, 1961 2 Sheets-Sheet 2 Ag F/'g. 5

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ATTORNEYS United States Patent 3,153,164 COMMUTATOR BRUSH AND CONNECTIONRoman Mariam Jop, Cleveland, Ohio, assignor to Kirkwood CarbonCorporation, Cleveland, Ohio, :1 corporation of Ohio Filed May 15, 1961,Ser. No. 109,908 7 Claims. (Cl. 310-249) This invention relatesgenerally to contact brushes for use in electrical apparatus, and morespecifically to improved connections between such brushes and theflexible conductors which conduct electric current to and from thebrushes.

Heretofore, it has been conventional practice to either fasten an end ofthe conductor (commonly referred to as a shunt or pig-tail) to a'metal'rivet or bolt which is secured in the body of the brush, or toinsert the end of the shunt into a hole drilled in the brush and thentamp into the hole suitable metal powder. However, neither of thesecommon constructions has been wholly adequate in maintaining a tight,low resistance shunt connection under the continuous vibration to whichthe brushes are normally subjected, and in resisting failure underadverse operating conditions, such as overload, high temperatures, andthe like, which cause high brush temperatures.

For example, in the conventional rivet-type brush construction, themetal rivet expands and contracts in response to temperature variationsmore rapidly than will the brush, which usually is composed of graphiteor carbon, or a mixture thereof with a metal such as copper. Theresulting movementof the rivet relative to the brush causes theconnection to loosen, therebyproducing increased electrical resistanceand undue heating of the brush. i

Prolonged vibration of tamped shunt constructions usually loosens themetal powder and produces increased electrical resistance. Moreover,when the compacted powder of the connection loosens, air is able topenetrate into the interstices to cause deleterious oxidation of thepowder at elevated temperatures.

Prior attempts to overcome the foregoing difficulties, such as using asilver powder to form tamped shunt connections and metallizing the brusharound the rivet in the rivet-type brush constructions, have beenlargely unacceptable from, a commercial standpoint because of the highmanufacturing costs which are entailed.

An object of the present invention is to provide an improved shuntconnection for electrical brushes.

A more specific object of the invention is to provide a mechanicallystrong, low resistance shunt connection which will withstand prolongedvibration without loosening and which will not deteriorate under severeoperating conditions such as heat, overload and the like.

Another object of the invention is to provide a shunt connection havingthe above described advantages which may be inexpensively manufacturedwithout requiring the high degree of operator skill necessary in formingthe prior tamped metal powder type of connections.

Other objects and advantages of the invention will become apparent fromthe following detailed description and the accompanying drawings.

In the drawings:

FIGURE 1 is an exploded view illustrating a preferred manner of forminga shunt connection in accordance with the present invention.

FIGURE 2 is a front elevational view of the preferred embodiment of theinvention.

FIGURE 3 is a cross-sectional view taken along the line 3-3 of FIG. 2.

FIGURE 4 is a cross-sectional view of another embodiment of theinvention.

FIGURE 5 is a cross-sectional view of a brush having compressed betweenthe 3,153,164 Patented Oct. 13., 1964 ICC a button inserted therein andshowing a cement bond between the brush and button.

FIGURE 6 is a cross-sectional view of a button having a portion providedwith a thin metal coating according to this invention.

Referring first to FIGS. 1, 2 and 3, reference numeral 10 designates abrush which consists essentially of carbon or graphite, or a mixturethereof with metal. The brush 10 is shown as having a concave endsurface 11 which may be held by conventional means in sliding contactwith the commutator or contact ring of an electrical apparatus.

In accordance with the preferred embodiment of .the invention, a hole 12is drilled through the brush from its front to back surface, The hole 12is counterbored from one surface of the brush for approximatelythree-quarters of the brush thickness to form an enlarged recess 13..The bottom of the recess 13 defines a shoulder 14. A

second hole or passage 15 is anguiarly drilled through the top surfaceof the brush 10 into communication with the recess 13 at the shoulder14.

A shunt or pig-tail 16, which is usually formed of twisted or braidedcopper wires, is doubled on itself within the recess 13 to form a loop17 and isthere securely clamped by a button 2 1 to form a tightelectrical connection with the brush. The free ends of the shunt are fedout of the brush body through the passage 15 and may be twisted togetherin the manner illustrated in FIGS. 2 and 3.

As shown, the button 21 has stem 22, which is formed to fit tightly intothe hole 12, and a head 23 of approxiinately the same diameter as therecess 13. The axial length of the head 23 is less than the depth of therecess 13 so that the button stem 22 can be inserted through the loopedportion 17 of the shunt and the loop 17 tightly end and the recessshoulder 14.

a As may be seen in FIG. 5, the button 21 is fixedly secured in itsassembledposition within the brush by a suitable cement 50, whichperferably is conductive.

Instead of being formed of metal, as are the rivets in conventional,rivet-type brush constructions, the button 21 consists of the samematerial as the body of the brush 10. By reason of this construction,the button will experience the same degree of expansion as the body ofthe brush when it is heated, and therefore will have no tendency undersevere operating conditions to loosen and produce a defective connectionof high electrical resistance.

As is illustrated in FIG. 6 of the drawings, the invention contemplatesa slightly modified button construction in which the stem 22 is providedwith a thin metal coating 60 consisting of copper, silver or the like.In addition to having substantially the same rate of thermal expansionand contraction as the body of the brush, this latter construction ofthebutton 21 results in the formation of an optimum electricalconnection between the shunt 16 and the brush. As distinguished from therelatively expensive prior art practice of me'tallizing the brushesaround the rivets in conventional rivet-type brush constructions, thebutton stems 22 of the present invention may be inexpensivelyelectroplated by well-known procedures.

Another important advantage of the illustrated construction is thesimplicity and ease with which the reliable, mechanically strong and lowresistance shunt connection of the invention can be formed. Whenpreparing the connection, all that is necessary is to drill. the holes12 and 15 and the counterbore 13 and separately form the button 21. Theshunt 16 may be then doubled on itself in the recess 13 to form theloop1'7 around the side wall of the recess and the free ends of theshunt fed radially outwardly through the passage 15. The connection iscompleted by forcing the button stem 22 through the loop 17 into thehole 12 until the head 23 is constrained within the recess 13, and theloop is slightly flattened against the recess shoulder 14.Alternatively, the shunt 16 may be wrapped around the stem of the buttonand the button then inserted into the recess to compress the shuntbetween the head of the button and the shoulder of the recess.Preferably the cement Si is applied to the button stem before insertingit into the hole 12. As a final step, the outer surfaces of the buttonstem and head may be machined to insure that they are flush or slightlyrecessed from the respective back and front faces of the brush.

When the button is forced into assembled position, the looped portion 17of the shunt is tightly pressed against the shoulder 14 with the highdegree of uniform pressure necessary to provide an optimum conductingpath of low resistance between the brush and the shunt. Since the buttonwill expand and contract with temperature changes the same as the bodyof the brush, the clamping pressure exerted on the shunt will remainconstant regardless of changes in the brush temperature, therebyassuring a uniform, optimum conducting path under all operatingconditions.

FIGURE 4 illustrates a modified form of the invention. In thisembodiment of the invention, a hole or recess 33, which corresponds tothe recess 13 shown in FIGS. 1-3, is drilled into the brush 3th from oneface thereof. A slanting hole or passage 35 is drilled through the topof the brush into communication with the recess 33 at its bottom surface34.

A shunt (not shown) is looped within the recess 33 in the same manner aswas the shunt 16 in the preferred embodiment of the invention and thefree ends of the shunt fed radially outwardly through the hole orpassage 35. The looped portion of the shunt is then securely clampedwithin the recess by inserting the button 41.

The button 41 substantially corresponds to the previously describedbutton 21 except for a relatively short stem 42 which, during theassembly operation, is cemented to the bottom of the recess. The lengthof the stem 42 is such that the loop of the shunt will be slightlyflattened against the bottom 34 of the recess and tightly clamped with auniform pressure by the button head 43 when the stem 41 is assembledagainst the bottom of the recess. As in the case of the preferredembodiment of the invention, the button 41 is formed of the samematerial as the brush so that it will have the same rate of thermalexpansion and contraction, and, if desired, may be coated with asuitable metal around its stem 42.

The connection may be prepared by applying a drop of cement to thebottom of either the button stem 42 or the bottom 34 of the recess,inserting the stem through the looped portion of the shunt, and finallyforcing the head of the button into the conforming recess until the endof the stem is against the surface 34. As noted above, the length of thestem is such that the shunt will be pressed against the surface 34 bythe head of the button to form a satisfactory conducting path. As afinal step, the outer surface of the button head 43 may be machined sothat it is flush or slightly recessed from the surrounding surface ofthe brush.

In both embodiments of the invention, the shunt connections are sealedwithin the brushes by the buttons which, as noted above, remain tightlyfixed in their assembled positions. As a result, there is little chancethat oxidation or contamination of the connection will occur when thebrushes are exposed to elevated temperatures and deleterious atmosphericconditions.

Many other modifications and variations of the invention will obviouslybe apparent to those skilled in the art in view of the foregoingdetailed disclosure. Therefore, it is to be understood that, within thescope of the appended claims, the invention may be practiced otherwisethan as specifically shown and described.

What is claimed is:

1. An electrical contact brush comprising a solid body having a recessformed in one side and a separate passage extending into said recessfrom another side of the body, a shunt extending through said passageinto said recess, a shunt-securing button formed of the same material assaid body, said button having a head tightly constrained within saidrecess and a stem extending toward the bottom of said recess, said shuntbeing looped around said stem and pressed against the bottom of saidrecess by the head of said button to form a tight, mechanically strong,electrical connection of low resistance between the shunt and the bodyof the brush.

2. The brush as claimed in claim 1 wherein said body and button consistessentially of a carbonaceous material.

3. An electrical contact brush comprising a solid body having a holeextending therethrough from one side to an opposite side, said holebeing countcrbored partially through said body from said one side toform an enlarged recess, said body being further provided with aseparate passage extending into said recess from another side of thebody, a shunt extending through said passage into said recess, a buttonformed of the same material as said body, said button having a headconstrained within said recess and a stem tightly fitted within saidhole, said shunt being looped around a portion of said stern and pressedagainst the bottom of said recess by said head to form a tight,mechanically strong electrical connection of low resistance.

4. The brush as claimed in claim 3 wherein said brush and button consistessentially of a carbonaceous material.

5. An electrical brush comprising a solid body having a recess formed inone side and a separate passage extending radially outwardly from saidrecess to another side or" said body, and a button formed of the samematerial as said body, said button including a head tightly constrainedwithin said recess and a stern extending toward the bottom of saidrecess into engagement with said body, said head having an axial lengthless than the depth of said recess so that a shunt can be looped aroundsaid stem and clamped with uniform pressure against the bottom of saidrecess to form a tight, mechanically strong electrical connection of lowresistance.

6. The brush as claimed in claim 4 wherein the carbonaceous material isgraphite.

7. The brush as claimed in claim 6 wherein the button stem has 'a thincoating of metal selected from the group consisting of copper andsilver.

References Cited in the file of this patent UNITED STATES PATENTS1,122,432 Shaw Dec. 29, 1914 1,258,657 Cuthbert Mar. 12, 1918 1,681,081Bailey Aug. 14, 1928 2,569,059 Huff Sept. 25, 1951

1. AN ELECTRICAL CONTACT BRUSH COMPRISING A SOLID BODY HAVING A RECESSFORMED IN ONE SIDE AND A SEPARATE PASSAGE EXTENDING INTO SAID RECESSFROM ANOTHER SIDE OF THE BODY, A SHUNT EXTENDING THROUGH SAID PASSAGEINTO SAID RECESS, A SHUNT-SECURING BUTTON FORMED OF THE SAME MATERIAL ASSAID BODY, SAID BUTTON HAVING A HEAD TIGHTLY CONSTRAINED WITHIN SAIDRECESS AND A STEM EXTENDING TOWARD THE